In a process of manufacturing semiconductors, a wafer that is a plate-like article having a surface on which semiconductor devices or electronic parts are formed is electrically tested in a probing step, and then divided into individual chips (also referred to as dice or pellets) in a dicing step. The individual chips are then die-bonded to a part base in a bonding step. After die-bonded, the individual chips are resin-molded to be semiconductor devices or electronic parts in finished form.
As shown in FIG. 3, after a probing step, a wafer W is stuck at a back surface on an adhesive sheet (also referred to as a dicing sheet or a dicing tape) S having an adhesive layer formed on one surface and having a thickness of about 100 μm, and mounted to a rigid ring-shaped frame F. The wafer W in this state is conveyed in a dicing step, between the dicing step and a die-bonding step, and in the die-bonding step.
In the dicing step, a dicing device is used that grooves the wafer W with a thin grindstone called a dicing blade to cut the wafer W. The dicing blade is a thin grindstone on which fine diamond abrasive grains are electrodeposited by Ni, and an extremely thin dicing blade is used having a thickness of about 10 μm to 30 μm.
The dicing blade is rotated at high speed of 30000 to 60000 rpm to cut into the wafer W and completely cut the wafer W (full cut). At this time, the adhesive sheet S stuck to the back surface of the wafer W is cut into about 10 μm only from a front surface thereof. Thus, the wafer W is cut into individual chips T, but the individual chips T do not come apart and an arrangement of the chips T is not deformed, thereby generally maintaining the form of the wafer.
Laser-dicing is also proposed that applies laser light having a convergent point in a wafer W to form a modification area in the wafer by multiphoton absorption, and cuts the wafer W starting at the modification area, instead of using a dicing blade. For the laser-dicing, the wafer W is diced in the state as shown in FIG. 3, and thus an arrangement of chips T is not deformed, thereby generally maintaining the form of the wafer.
For the sake of convenience, a cluster of the chips T without the arrangement of the chips T being deformed is also herein referred to as a wafer W even after the wafer W is diced and divided into the individual chips T.
Then, the wafer W is fed to the die-bonding step. In the die-bonding step, a die bonder is used. In the die bonder, the wafer W is first placed on an expanding stage, and then the adhesive sheet S is expanded to increase spacings between the chips T so that the chips T can be easily picked up.
Next, the chips T are pushed up from below by a pusher and picked up by a collet from above to bond the chips T to predetermined positions on the base.
Such an expanding device that stretches an adhesive sheet S to increase spacings between chips T has been incorporated in a die-bonder. Various improvements of such an expanding device have been made (for example, see Japanese Patent Application Laid Open No. 7-231003, Japanese Patent Application Laid Open No. 7-321070, and Japanese Patent Application Laid Open No. 2001-024010).
In the related arts, a wafer W mounted to a frame F through an adhesive sheet S is cut into individual chips T by a dicing blade, conveyed as it is through a dicing device and cleaned, then conveyed to a die bonder, and also conveyed as it is through the die bonder.
However, in recent semiconductor devices such as ICs, a width of a machining area (also referred to as a street) for dicing has become extremely narrow in order to increase the number of chips formed from one wafer W. Thus, an extremely thin dicing blade having a thickness of about 10 μm to 15 μm has been used in a dicing step.
In a wafer W diced by such an extremely thin dicing blade or the above described laser-diced wafer W, spacings between chips T are extremely narrow, and if the wafer W is conveyed while being mounted to a frame F through an adhesive sheet S as is conventional, edges of adjacent chips T come into contact with each other by vibration during the conveyance to cause chipping or microcracks in the edges, thereby degrading good chips T or compromising reliability of finished products.
Thus, it has been required that a wafer W is expanded immediately after dicing in a dicing device, and conveyed with spacings between chips T being increased. However, even if the conventional expanding method or the expanding method described in Japanese Patent Application Laid Open No. 7-231003 or Japanese Patent Application Laid Open No. 7-321070 is performed in the dicing device, the wafer W cannot be conveyed together with the frame F because the expanded adhesive sheet S shrinks to its original shape when tension to the adhesive sheet S is released.
The invention has been achieved in view of the above described circumstances, and has an object to provide an expanding method and an expanding device of an adhesive sheet that allow even a wafer having extremely narrow spacings between chips after dicing to be conveyed together with a frame without edges of adjacent chips coming into contact with each other by vibration during the conveyance to cause chipping or microcracks in the edges.